An investigation was conducted of the rate, mechanism and stoichiometry of phosphate precipitation with aluminum and ferric salts from pure phosphate solutions and secondary effluent. These studies showed that the reactions of orthophosphate ion with both Al(III) and Fe(III) are completed in less than 1 second. The effects of pH, reactant concentration, and reagent aging on the efficiency of phosphate removal were evaluated in batch precipitation experiments. The pH of optimum orthophosphate precipitation was found to be close to 6.0 for Al(III) and in the vicinity of 3.5 to 4.0 for Fe(III). At constant pH, with both Fe(III) and Al(III) up to about a 1:1 molar ratio, orthophosphate removal was directly proportional to amount of added cation, indicating occurrence of a chemical reaction. Dilute solutions of Fe(III) were found to undergo extensive hydrolysis on aging with a resultant loss of capacity to precipitate phosphate. The removal of condensed phosphates by precipitation with aluminum and iron salts was found to be strongly dependent on pH and the reactant concentration ratio. Precipitates obtained in the reaction of orthophosphate with aluminum and ferric salts were examined by X-ray diffraction analysis after drying and heating to 104C and to 600C. Both precipitates remained amorphous, except that ferric phosphate was identified after ignition at 600C. (WRSIC abstract)